1. Field of the Invention
This invention relates, generally, to fuel cell stacks and, more particularly, to fuel cell stacks incorporating fuel cell basic unit(s) using special gas diffuser/collector plates.
2. Description of Related Prior Art
Attempts have been made in the past to introduce a better gas diffuser/collector plate. Several related patents have addressed the issue. Thus, U.S. Pat. No. 6,099,984, dated Aug. 8, 2000 and granted to Rock for a xe2x80x9cMirrored serpentine flow channels for fuel cellxe2x80x9d discloses a fuel cell using serpentine flow field channels. Thus, the input/inlet legs to each channel border the input/inlet of the next adjacent channels in the same flow field, and the output/exit legs of each channel borders the output/exit of the next adjacent channels in the same flow field. These type of channels is said to have one major disadvantage. The serpentine flow field channels in order to provide a uniform flow of fluid, requires an external increase of power. U.S. Pat. No. 6,048,633 dated Apr. 11, 2000 and granted to Fuji, et al., for a xe2x80x9cFuel cell stackxe2x80x9d discloses a fuel cell stack comprising a first and second separators for holding a fuel cell therebetween. The first separator has a fuel gas flow passage and the second separator has an oxygen flow passage. The gas flow passages are formed by grooves, the number of grooves decreasing from the inlet to the outlet. In one embodiment, the gas flow passage comprises twelve individual gas flow passage grooves, which communicate with an inlet hole on gas inlet side, six individual second gas flow passage grooves which communicate with first gas flow passage grooves and three individual third gas flow passage grooves which communicate with the second gas flow passage grooves. The third flow passage grooves communicate with an outlet hole on a gas outlet side. The main disadvantage of the above separators resides in the fact that the surface occupied by the flow field, due to the use of grooves with constant cross section, is relatively large. U.S. Pat. No. 5,773,160 dated Jun. 30, 1998 and granted to Wilkinson et al. for an xe2x80x9cElectrochemical fuel cell stack with concurrent flow of coolant and oxidant streamsxe2x80x9d, describes a fuel cell stack having an anode, a cathode and cooling plates. Each plate comprises channels for directing a fluid stream from an inlet to an outlet. The coolant stream channels extend such, that in operation, the coolest region of the cooling plate coincides with the region of the cathode layer having the highest concentration of oxygen (and/or the lowest water content), and the warmest region of the cooling plate coincides with the region of the cathode plate having the lowest concentration of oxygen (and/or the highest concentration of water). The fuel stream channels extend such, that in operation the fuel stream is directed to a region of the cathode plate in which the oxidant stream has the lowest concentration of oxygen (and/or the highest concentration of water), and is subsequently directed to a region of the anode plate which coincides with the region of the cathode plate in which the oxidant stream has the highest concentration of oxygen (and/or the lowest water content). In its plate""s configuration, Wilkinson et al., structure has an essential shortcoming. The channels having a constant cross section require an elevated pressure and hence, significant power is required.
There is accordingly a need for a fuel cell stack, which overcomes the above-mentioned disadvantages of prior art.
Thus, it is the primary objective of the present invention to provide an efficient fuel cell stack.
It is another objective of the present invention to provide a compact fuel cell stack.
Broadly stating, the fuel cell stack according to the present invention comprises at least one fuel cell basic unit containing a gas diffuser/collector plate serving as an anode, an ion exchange membrane disposed on top of the gas diffuser/collector plate and an air diffuser/collector plate serving as a cathode and disposed on top of the ion exchange membrane.
The gas diffuser/collector plate has a face directed to the ion exchange membrane which face is provided with a flow field incorporating a multiplicity of adjacent open faced flow channels. Each open-faced flow channel has a cross-section continuously diminishing from its inlet to its outlet, so the flow field, viewed from the top, forms a trapezoidal contour. The fuel cell stack further includes: a reactant manifold plate placed on the gas diffuser/collector plate, an oxidant manifold plate disposed on the reactant manifold plate, a first end sealing plate disposed beneath the gas diffuser/collector plate and a second end sealing plate disposed on top of the oxidant manifold plate. Furthermore, a fastening means is used.
The first and second end sealing plates, the reactant and oxidant manifold plates are all preferably provided with means for accommodating the fasteners.
In one aspect of the invention, the fuel cell stack, ion exchange membrane, air diffuser/collector plate, reactant and oxidant manifold plates, and the first and second end sealing plates are essentially similar in shape with the gas diffuser/collector plate. The assembled fuel cell stack has, basically, a trapezoidal form.
In another aspect of this invention, the fuel cell basic unit used in the above fuel cell stack has a gas diffuser/collector plate provided with a face directed to the ion exchange membrane. The face is provided with a flow field incorporating a multiplicity of adjacent open-faced flow channels has a cross section continuously diminishing so that larger and narrower ends are formed. Thus the flow field, viewed from the top forms a trapezoidal contour.
In another aspect of this invention, all the larger ends of the multiplicity of open-faced flow channels are adjacent to a wider side of the contour, while all the narrow ends of the multiplicity of the open-faced flow channels are adjacent to a narrow side of the contour. Each larger end of each open-faced flow channel is inclined with respect to the wider side of the contour, while each narrow end of each open-faced flow channel is inclined with respect to the narrow side of the contour.
In yet another aspect of the present invention, proximate to each extremity of the larger end of each open-faced flow channel, an inlet port is provided: a first inlet port, situated in the interior of each open-faced flow channel and a second inlet port, situated outside each open-faced flow channel.
All first and second inlet ports are collinear.
Proximate to each extremity of the narrow end of each open-faced flow channel an outlet port is disposed. A first outlet port is disposed in the interior of each open-faced flow channel; a second outlet port is disposed outside each open-faced flow channel.
All first and second outlet ports are collinear.
In a first variant of the gas diffuser/collector all large ends of all open-faced flow channels are adjacent to a wider side of the contour. All narrow ends of all open-faced flow channels are adjacent to a narrow side of the contour. Each large end of each open-faced flow channel is inclined with respect to the wider side of the contour. All narrow ends of the open-faced flow channels communicate directly with a common recess. In the latter a drain hole is located. Outside the common recess a gas-expelling aperture is disposed. Proximate to each extremity of the large end of each open-faced flow channel an inlet port is provided: a first inlet port situated in the interior of each open-faced flow channel, a second inlet port situated outside each open-faced flow channel. All first and second inlet ports are collinearly located.
In a second variant of the gas diffuser/collector, a supply recess is located near all larger ends. In a wall of the supply recess, close to the large end, a series of communicating holes is provided. The latter connects the supply recess with the open-faced flow channels. In the supply recess a supply hole is disposed. Outside supply recess a gas supply aperture is located. All the narrow ends of all the open-faced flow channels communicate directly with a common recess. In the interior of the latter a drain hole is placed. Outside the common recess a gas-expelling aperture is provided.